As is well known, data capture circuits are commonly used in a wide variety of integrated circuit applications. A significant drawback of conventional data capture circuits is the difficulty associated with measuring the ability of such circuits to capture data. For example, flip-flops, memory cells, latches and other data capture elements of such circuits often have minimum requirements for set-up and hold times. The set-up time refers generally to the period of time that the data must maintain a particular logic level at a circuit input prior to clocking, while the hold time refers to the amount of time that the data must remain at the particular level at the circuit input after clocking. The minimum requirements for the set-up and hold times must be satisfied in order for the particular data level to be reliably captured by the circuit.
In accordance with conventional techniques, the minimum set-up and hold time requirements are typically measured using specialized test equipment. Unfortunately, such test equipment can be expensive, and the time associated with the test process itself further increases the cost of circuit design, development and manufacturing. In addition, even the most sophisticated conventional test equipment has only limited accuracy, e.g., may be able to determine the minimum set-up and hold time requirements for a given data capture circuit only down to an accuracy of about +/−150picoseconds. In many applications, it would be desirable to determine the set-up and hold time requirements to an accuracy of about +/−10 or +/−20 picoseconds, but as indicated above, the conventional test equipment is unable to provide this accuracy.
It is also known in the art to configure certain types of data capture circuits so as to be less sensitive to variations in data signal transitions. Examples of such techniques are described in U.S. patent application Ser. No. 09/374,258 filed Aug. 13, 1999 in the name of inventors T. J. Gabara et al. and entitled “Signal Processing Method and Apparatus For Ensuring a Desired Relationship Between Signals,” which application is commonly assigned herewith and incorporated by reference herein. However, these techniques do not adequately address the data capture measurement issues identified above.
A need therefore exists for an improved data capture circuit which eliminates the problems associated with conventional specialized test equipment, while providing enhanced accuracy for measurement of minimum set-up and hold time requirements.